Chain oil leakage could be due one of a number of things.
•Have you overfilled the oil reservoir? It’s easy to do and it is amazing how many times this simple oversight is the cause of chain oil leaks. An overfilled reservoir can often leak oil when the saw is turned on. Check this and siphon some off if it looks excessively high. Then power up the saw and see if the leak has subsided.
•An over-oiled guide bar can also cause leakage. To prevent this, remove the chain and clean the bar with a dry cloth. Then power up the saw and see if it stops
•Possibly the fill plug is not sealing or the oil is leaking through the chain oiling line.
•Clogged oil outlets around the clutch and sprocket can cause leaks if dust or sawdust has got into them. Clean them out thoroughly and then operate to check if the leak is still there. Your manual will show you where they are on your particular Chainsaw
•Look at the filler cap and check to see if it has worn out or become faulty or if the seal has been broken. Replace if so.
•Even after you have emptied the reservoir, the leak could continue if the pump is dirty or clogged. Check the pump gaskets for wear and wipe clean. Replace if necessary
•If the oil is running out via the delivery line to the bar then there is a chance that the tank vent is plugged up. If so, the chain may be running 'dry' during operation. Check the vent (see your manual for location) You can clean blocked plugs with wire and an aerosol spray WD40, etc.
Engineer’s Tip – If you want to find out whether your chain is being oiled properly, place a piece of white card or paper on the ground/floor, point the chainsaw down towards it (being careful not to touch the ground) and just rev’ it a little bit. If there is adequate oil on the chain, a fine mist should spray from the guide bar/chain marking the card or paper.